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NEW YORK STATE MUSEUM 



interest. The investigation has progressed sufficiently to permit the 

 restoration of all the hard anatomy of the principal genera of the 

 order. Stylonurus, which has been known as one of the largest 

 of these creatures, attaining a length of 5 — 6 feet, proves, on study 

 of smaller species from Otisville, materially different in structure 

 from the generally accepted restoration. It has also been possible 

 to restore the genera Eusarcus and Dolichopterus with all their 

 appendages and to assemble all parts, of the integument of the 

 largest Pterygotus occurring in the New York formations. Other 

 results of significance are the recognition of the genus Drepanop- 

 terus; the identity of the eve structure of Pterygotus with that 

 of Limulus shown by the presence of an outer smooth thick 

 cornea which is separable from an inner layer of lenses ; the 

 demonstration that the chelicerae of Pterygotus consist of long 

 unjointed arms carrying the terminal pincers; and the close relation- 

 ship of the genera Stylonurus and Dolichopterus brought out by 

 transitional forms and the identity of new structures observed in 

 their New York representatives. 



The genus Stylonurus is resolved into three subdivisions for 

 which the subgeneric terms Stylonurus sensu stricto, Ctenopterus 

 and Homalopterus are introduced. These divisions are based 

 mainly on the character of the legs. 



The genus Hughmilleria has been shown to agree in the struc- 

 ture of its compound eyes with Eurypterus, although the position 

 of these suggests a closer relationship to Pterygotus. 



The Cambric genus Strabops possesses the full complement of 

 12 dorsal segments instead of II, as hitherto supposed, and has 

 small compound eyes placed far back and near the lateral margin. 

 The investigation of the larval forms of a number of Siluric species 

 has shown that some of these pass through a stage identical in its 

 most important features with the adult Cambric Strabops. 



The ontogeny of Eurypterids is for the first time investigated and 

 the development of species of the genera Eurypterus, Eusarcus, 

 Hughmilleria, Pterygotus and Stylonurus is traced as far back as 

 the nepionic or larval stage, and a number of larval characters 

 arc established which appear to be common to all and of signifi- 

 cance in phylogenetic relation. 



Both the restorations of the genera and the investigation of the 

 ontogeny have allowed conclusions on the phylogeny of the 

 Eurypterids, as well as their morphology and mode of life. 



